Organic EL displays are typically driven by active matrix circuitry in order to produce high performance devices. In an active matrix configuration, each pixel is driven by multiple circuit elements such as two or more transistors, one or more capacitors, and signal lines. For multicolor devices, a pixel is divided into subpixels each with a complete set of circuit elements. For a RGB (red, green, blue) device, each pixel consists of three subpixels, which emit red, green, and blue light. Examples of such active matrix organic EL devices are provided in U.S. Pat. Nos. 5,550,066; 6,281,634; and 6,456,013; and EP 1102317.
When manufacturing organic EL displays, problems such a particle contamination or scratches in the organic EL materials from the various process steps such as shadow masking may result in defects in a display. One type of defect that is caused by particle contamination or scratches is a short circuit through the thin organic materials, connecting the anode and the cathode. A short between the anode and cathode results in a non-emitting pixel.
Many defects, such as particle contamination and scratches, typically occur with an area density that depends on the capability of the manufacturing process and equipment. However, the total yield with respect to non-emitting pixels depends on the area density of the defects and the area of the individual displays. Larger displays such as those useful for televisions, computer monitors, or laptops, will have lower yields than smaller substrates given the same defect density.